From the photos that appears to be a pin connected truss... a long obsolete (but not unknown) design, likely dating to near 1900... This can lead to issues... how to make repairs, what other things need to be inspected (likely the pins) would it be easier to just replace it with a modern design, but if so, is it a protected historic resource...
Also to be noted, the river is a protected resource... we are likely at high water and based on this years snow pack may be at high water for some months... they you may need a permit to work in the stream to protect the eco-system... an eco-system previously badly damaged by a previously damaged by a train derailment...
Randy Hees